System and Method for Analyzing Dusty Industrial Off-gas Chemistry

ABSTRACT

An off-gas analyzer for analyzing H 2 O vapor, CO, O 2 , CO 2  and/or H 2  in a furnace gas stream is fluidically coupled to a gas extraction probe. The analyzer includes an optical measurement cell having multiple sampling chambers, optically coupled to a laser. The analyzer measuring cell is housed within a heated cabinet having a heater operable to heat the interior thereof so as to maintain the extracted gas sample therein at a temperature about the condensation point of water. The analyzer allows for the analysis of the gas water vapour of wet off-gas samples.

RELATED APPLICATIONS

This application claims priority and the benefit of 35 USC §119(e) toU.S. Provisional Patent Application Ser. No. 62/037,821, filed 15 Aug.2014, the disclosure of which is incorporated herein by reference.

SCOPE OF THE INVENTION

The present invention relates to a system and method of analyzingoff-gases, and more particularly a system for the analysis of dusty orhigh-particulate industrial off-gas chemistry by performing the opticalanalysis of one or more off-gas components in proximity to an off-gasflue.

BACKGROUND OF THE INVENTION

Technology that continuously analyzes off-gas chemistry is an importanttool for optimizing, controlling and improving the performance ofcombustion processes such as electric arc furnace (EAF) and basic oxygenfurnace (BOF) steelmaking processes or the like.

In the EAF steelmaking process, full-spectrum off-gas analysis for CO,CO₂, H₂, O₂, H₂O vapor and N₂ is a valuable tool for holisticoptimization and control of the steelmaking process.

-   -   N₂ analysis is effective for assessing and dynamically        controlling fume system suction to avoid both over and under        drafting conditions    -   CO, H₂, O₂ & N₂ analysis are effective for determining if the        EAF is operating in an overly oxidizing or reducing atmosphere    -   CO, CO₂ & H₂ analysis are effective for optimizing and        dynamically controlling burners and for optimizing the charge        carbon practice    -   CO & CO₂ analysis are effective for optimizing and dynamically        controlling carbon injectors    -   CO, H₂ & O₂ analysis are effective for optimizing and        dynamically controlling the oxygen lances    -   H₂ & H₂O vapor analysis are effective to determining the onset        of a water panel leak into the furnace    -   CO, CO₂, H₂, O₂, H₂O vapor and N₂ analysis is required to close        a real-time mass & energy balance for the EAF process

Similarly, in the BOF steelmaking process having a full spectrum off-gasanalysis for CO, CO₂, H₂, O₂, H₂O vapor and N₂ is preferred to close areal-time mass & energy balance for the BOF process which is effectivefor controlling the efficiency of the oxygen blowing practice,controlling the amount and the timing of post combustion oxygen flow anddetermining when to terminate the oxygen blow because the aim steelcarbon and temperature endpoints have been achieved.

To date, continuous off-gas analysis technology for industrialapplications has remained essentially unchanged since about 1997 beingbased on one of two principle methods;

-   1. Extractive systems use a vacuum pump to continuously extract a    sample of process off-gas through a probe positioned in the fume    duct with said probe connected to a hollow often heated conduit that    directs the off-gas sample to a continuous gas analyzer. E. J.    Evenson U.S. Pat. No. 5,777,241 describes such an extractive system    for optimization and control of steelmaking processes. Depending on    the gaseous species to be analyzed, various analytical methods are    employed with extractive technology including mass spectrometry    which can analyze most gaseous species, non-dispersive infra-red    (NDIR) which is a standard method for analyzing CO and CO₂, a solid    state electrochemical cell and thermal conductivity which are    standard methods for O₂ analysis and for H₂ analysis respectively.-   2. In situ laser systems transmit a single beam or a combined beam    or multiple individual beams within the visible, near and mid IR    range through the off-gas as it flows in the fume duct for    subsequent pick-up by an optical detector(s). D. K. Ottesen U.S.    Pat. No. 5,984,998 and S. C. Jepson U.S. Pat. No. 6,748,004 present    examples of in situ laser systems for measuring off-gas chemistry.    In general, the transmitted lasers wavelength is modulated around    the particular spectroscopic line of the gaseous species of    interest. The amount of absorption in the detected beam is    subsequently used to calculate the concentration of that particular    species in the off-gas. Multiple lasers are required depending on    the gaseous species to be analyzed, typically one near IR range    laser with a suitable wavelength for CO₂ and H₂O vapor, a second    near IR range laser with a suitable wavelength for CO and a third    visible range laser with a suitable wavelength for O₂. It is noted    that three separate lasers of the correct wavelength are required to    analyze CO, CO₂ and O₂. Because the CO and CO₂ absorption peaks    begin to overlap as the off-gas temperature increases above about    300° C., in situ laser systems need to employ one near-IR range    laser with a suitable wavelength for CO₂ and a separate second    near-IR range laser for CO. A third visible range laser with a    suitable wavelength is required for O₂. The in situ method can also    utilize either the CO or CO₂ laser to analyze H₂O vapor if required.    Because varying amounts of particulate matter are present in most    industrial process off-gas, there is the possibility that the laser    beam will suffer from attenuation which will scatter or block the    beam. In many industrial applications, said attenuation problems can    be reduced but not completely eliminated by employing two horizontal    or vertical probes that are continuously purged with an inert gas    such as N₂ with one probe housing the laser beam emitters and the    second probe housing the laser beam detectors. These two probes    extend into the fume duct from opposite sides with one probes open    end being in close proximity to the opposite probes open end which    serves to reduce the path length that the beams must successfully    traverse between emitter and detector and minimize laser beam    attenuation problems associated with particulate matter    interference.

Extractive and in situ laser technologies each have their respectiveadvantages and disadvantages and hence neither technology provides acomplete off-gas analysis solution;

-   -   Analytical Capabilities: Extractive off-gas systems have the        advantage of being able to utilize and combine a range of        analytical methods to provide a virtually complete spectrum of        off-gas chemistry. For example, steelmaking off-gas chemistry        consists almost exclusively of six gaseous species which vary in        concentration according to process dynamics; CO, CO₂, O₂, H₂,        H₂O vapor and N₂. For all practical purposes and unless a        foreign gas is deliberately introduced into the furnace        atmosphere, the concentration sum of these six gaseous species        totals 100%. As explained earlier, various extractive analytical        methods can be used to analyze for CO, CO₂, O₂, H₂ & H₂O vapor.        In the case of N₂, it can either be analyzed by extractive mass        spectrometry or it can be calculated with reasonable precision        by summing the analysis of the remaining five principle gaseous        species and subtracting from 100%.    -   By comparison in situ laser systems can use a combination of        lasers in the correct wavelength range to analyze specific        gaseous species of interest. For example, for in situ analysis        of high temperature off-gas such as for steelmaking        applications, three separate lasers of different wavelengths        will be required to analyze CO, CO₂, O₂ & H₂O vapor. However, in        situ laser technology is not technically capable of analyzing        many mononuclear diatomic gases including N₂ and H₂ (S.        Schilt, F. K. Tittel and K. P. Petrov, “Diode Laser        Spectroscopic Monitoring of Trace Gases”, Encyclopedia of        Analytical Chemistry, pages 1-29, 2011). Hence, compared to        extractive methods in situ laser technology has the disadvantage        of limited analytical capabilities.    -   Analytical Precision: Extractive systems can tailor their        analytical method to meet the analytical precision needed for        specific industrial process control situations. Hence,        extractive technology has the advantage of having the        flexibility to tailor the analytical precision to the        application requirements.    -   The analytical precision of laser systems is gas species        dependent. The amount of absorption of the beam determines the        analytical precision. Each gaseous species has an optimum beam        path length that provides the optimum amount of absorption and        the optimum analytical precision. In general, using a path        length with the optimum absorption will meet the analytical        precision needed for many industrial process control situations.        However, path lengths that are shorter than the optimum will        reduce the amount of absorption and the analytical precision.        Conversely, too long a path length can result in signal        saturation and limit the measurement span of the instrument. In        situ lasers use a fixed path length defined as the distance        between the laser beam emitter and detector. This fixed path        length is common to all gaseous species being analyzed. As        described previously, in situations where there are optical        signal transmission difficulties due to beam attenuation in        dusty industrial off-gas environments, in situ laser systems        select the fixed path length to minimize laser interruptions by        positioning two opposite facing inert gas purged probes. The        separation distance between the open ends of said two probes        defines the fixed path length that the laser beam must transmit        through the process off-gas. Hence, compared to extractive        methods which can be designed for high analytical precision for        all gaseous species, the fixed, common path length used in in        situ laser technology may or may not provide the required        analytical precision for all gaseous species being analyzed.    -   Calibration: Most extractive analytical methods require periodic        recalibration to compensate for analytical drift. Depending on        the gases to be analyzed, extractive systems can require several        specialized calibration gases which can be expensive. Hence,        extraction technology has the disadvantage that the analytical        methods require periodic recalibration and specialized        calibration gases.    -   In situ laser systems are often equipped with reference cells        that contain known concentrations of the gaseous species being        analyzed. Laser technology uses the known reference cell gas        composition to self-calibrate the system. Hence, compared to        extractive methods, in situ laser technology has the advantage        that it does not require periodic recalibration or specialized        calibration gases.    -   Analytical Response Delay: The analytical response delay for        extractive system depends on the residence time of the off-gas        sample from the probe tip to the analytical cells located in the        analyzer. The residence time is dependent on the volume of the        gas train (probe, transport conduit & filtration system), the        extraction flow rate of the gas and the physical distance        between the probe and the analyzer which is often longer than        desirable because of the need to house the analyzer in a large,        environmentally protective enclosure. While extractive systems        can use a high velocity pump to rapidly extract off-gas at high        flow rate through the probe, often the analytical devices inside        the analyzer are designed to use only a slower velocity gas flow        rates and therefore the majority of the off-gas extracted sample        is vented before the analyzer which uses only a slower velocity        slip stream. All of these factors serve to increase the        analytical response delay of extractive systems. Most modern        extractive systems for example those used in the steel industry        are designed to provide an analytical response within about 20        to 40 seconds from the time the gas enters the probe tip until        the corresponding gas analysis is reported. In situ laser        systems have a much shorter response delay of the order of 2        seconds because the off-gas is not physically transported to a        remote analyzer. Hence, compared to extractive methods in situ        laser technology has the advantage of a much shorter analytical        response delay.    -   Analytical Reliability: Extractive off-gas systems can be        categorized as “active” technology. Typically the extractive        analysis system is interfaced with the furnace control network        so that whenever the industrial process is producing off-gas,        the extractive system automatically switches on a pump or the        like to provide high suction to actively extract a sample of        off-gas through the probe which is appropriately positioned in        the fume duct. The off-gas sample is transferred at high flow        rate through a hollow heated or unheated conduit to the        analyzer. For dirty, humid off-gas as exists in many industrial        processes, the hot, humid off-gas sample is first passed through        a series of progressively finer filters to remove particulate        matter from the off-gas sample. Since many analytical techniques        mentioned previously require clean, dry gas for reliable        chemical analysis, after filtration the process off-gas is        typically passed through a condenser or the like to remove water        vapor prior to analysis which is subsequently reported on a dry        basis. In a few select situations such as when it is necessary        to avoid formation of corrosive acids in the condensate or when        analyzing some specific gaseous species such as water vapor, the        cleaned off-gas sample maybe kept at a temperature above its dew        point and analyzed wet. However, in such instances the        analytical cells must be designed to operate reliably and        precisely at elevated temperature. Extractive systems are        typically designed to automatically and periodically switch to        an active back-purge for example during periods when the        industrial process is not producing off-gas. This automatic        back-purge can consist of high pressure compressed air or inert        gases such as N₂ or the like and are designed to clean the probe        and filters of accumulated particulate matter. Historically,        such extractive technology that alternates between positive        suction and back-purging has demonstrated exceptional analytical        reliability, for example when properly maintained, extractive        technology applied for in harsh steelmaking process conditions        has reportedly demonstrated better than 99% reliability to        provide continuous off-gas chemistry from start-to-end of the        steel producing heat.    -   By comparison, in situ laser systems can be categorized more as        “passive” technology that relies on passive transmission of        laser beam(s) through the off-gas fume from an emitter to a        detector. Attenuation of the laser beam that prevents a        sufficient level of detection will result in interrupted off-gas        analysis. For example, under steelmaking process conditions,        early in situ laser systems suffered from serious laser beam        attenuation difficulties and lost signals because of significant        amounts of dust prevalent in the harsh process off-gas. As        discussed previously, various methods have been reported to        reduce attenuation difficulties including the use of continuous        inert gas purged, opposite facing horizontal or vertical probes        to shorten the path length that the laser must successfully        transmit through the dirty process gas, or, particulate        deflectors or impingers such as disclosed by W. A. Von Drasek        U.S. Pat. No. 6,943,886. While these devices have considerably        reduced beam attenuation problems compared to original full path        length in situ designs, because of the passive nature of laser        transmission there still remains a risk that one or more of the        in situ laser beams may suffer from periodic and unpredictable        interruptions in signal transmission especially when dust        loading is particularly high. For example, steel industry        reported information indicates that on average about 50% of EAF        heats will experience some degree of lost laser signals due to        fume signal interruption. Any lost laser signals during EAF        scrap melting would limit effectiveness of off-gas water leak        detection systems during critical melting periods when hung-up        scrap can fall into bath and create a metal slosh event that can        trigger a water leak related explosion. In addition laser signal        interruption limits the effectiveness of process monitoring and        control functions. Hence, compared to extractive methods in situ        laser technology has the disadvantage of uncertain analytical        reliability especially in harsh industrial situations such as        steelmaking processes.    -   Installation and Maintenance Considerations: Most extractive        analyzers used in harsh industrial situations must be housed        within a protective room or enclosure that ensures the        electronics are maintained within an acceptable working        environment particularly regarding minimizing industrial dust        and maintaining suitable ambient temperatures. If a suitable        enclosure does not already exist within the plant, a protective        room will need to be constructed which adds to the cost of        installation. To minimize analytical response delays, the        protective analyzer room needs to be located within close        proximity (usually with ˜30 meters) from the extraction probe.        Depending on the particular circumstances, finding a suitably        sized area in close proximity to the probe can be challenging in        confined industrial spaces. Because extractive systems filter        and usually dry the process off-gas prior to analysis,        extractive systems require regular maintenance to inspect and        replace clogged filters, to inspect and service pumps and        condensers as well as discussed previously, to periodically        check and adjust calibration to ensure analytical precision.    -   By comparison, in situ laser systems mount the laser beam        emitters and receivers on the fume duct often inside protective        path length shortening probes as discussed previously. The laser        beam is usually transmitted to the emitter from a remotely        located laser by fiber optic cable. The received signal after        the beam has passed through the process off-gas is also        transmitted electronically. As such, since the off-gas does not        physically transfer to the lasers and signal analysis        componentry, it can be located remotely without distance        restrictions. In addition, in situ systems do not require        filters, condensers or pumps. Hence, compared to extractive        methods in situ laser technology has the advantage of lower        installation costs and less maintenance requirements.    -   Process Control Functionality: The functionality of the off-gas        analysis technology for optimizing, controlling and improving        the performance of a combustion process will depend largely on        the analytical capabilities of the off-gas analysis system. For        example, the following table provides the key gaseous species        analyses required to provide complete process control and        optimization functionality in a steelmaking furnace. Hence        applicant has recognized the extractive methods which provide a        complete off-gas analysis spectrum have the advantage over the        limited analytical capability provided by in situ laser        technology.

SUMMARY OF THE INVENTION

In one aspect, the current invention involves a novel method neverbefore reported in the prior art for analyzing dust containing, hightemperature industrial off-gas. The current invention makes use of theadvantages of the extractive and in situ laser methods, while avoidingmany of their respective disadvantages as overviewed above. The novelaspects of the current invention as more fully described herein enableanalytical response times of as short as about 8 seconds, as well asuninterrupted full spectrum analysis of H₂O vapor, CO, O₂, CO₂ and H₂.

The invention provides in another aspect a system and method foranalyzing off-gases, and preferably high temperature industrial off-gas,such as for example, dust laden industrial off-gases from steel makingfurnaces, smelters and the like. The invention may enable analyticalresponse times of as short as 0.5 to 4 seconds in certain applicationsand/or more uninterrupted full spectrum analysis of a variety of off-gascomponents, including without limitation, H₂O vapor, CO, O₂, CO₂ and/orH₂.

Most preferably, the system includes an off-gas analyzer which iselectronically linked to plant or furnace control systems to regulate orvary plant or furnace operating parameters, in response to detectedoff-gas components.

In one embodiment, the system includes a suitably designed probe, andmore preferably a fluid cooled gas sampling probe and associated gasextraction pump. The probe and pump are used to intermittently orcontinuously extract an off-gas sample from a selected sampling pointalong the furnace or fume duct, and to convey the gas-sample to asampling station or analyzer for analysis. Although not essential, mostpreferably the extracted off-gas sample is a wet off-gas sample, withthe probe configured to extract gas samples from the furnace or fumeduct whilst maintaining the extracted gas sample at a temperatureselected to substantially prevent condensation of water vapour and/orgaseous phases therefrom. One preferred probe construction is describedin commonly owned International Patent Application No.PCT/CA2014/000162, entitled “Non-Condensing Gas Sampling Probe System”,the disclosure of which is incorporated herein in its entirety.

Where exhaust gas water vapour content is to be analysed, a hollowheated conduit is preferably also used to fluidically transfer the hot,wet off-gas sample from the probe to the analyzer/sampling station. In asimplified design, the heated conduit is provided with a resistance-typeheater and covering insulation to maintain the extracted gas sampletherein at an elevated temperature substantially preventing orminimizing water condensation therefrom. The sampling station mayoptionally include a heated gas sampling chamber which includes anoptical measuring cell maintained at an elevated temperature above a dewpoint or condensation temperature of selected off-gas components, andmost preferably a temperature of at least 100° C., and preferably about130° C.±10° C. The sampling station and optic measuring cell areoptically coupled to or provided with one or more coherent light sourcesor associated lasers. The lasers are operable to transmit coherent lightbeam energy to the measuring cell and through an extracted off-gassample for analysis of one or more gas sample component concentrations.In another possible construction, the measuring cells are preferablyoptically coupled to a TDL laser operable to emit a coherent light beamin the IR, and preferably mid-IR range, by way of a fiber optic cable.The measuring cells are operable to analyze CO, CO₂, O₂, water vapourand/or H₂ concentrations in the extracted gas sample.

In another embodiment of the system, a suitably designed water cooledsample probe and associated pump may be used to continuously forceextract a sample of off-gas from a fume duct. The water cooled probe hasits open end positioned inside the fume duct. To minimize the delay timeassociated with extracting the off-gas sample through the probe, in thepreferred embodiment of the current method, the probe incorporates acentrally located smaller diameter extraction line with the aperture ofsaid extraction line being extended downwards to be in close proximityto the opening of the main body larger diameter probe. By using anextended smaller diameter extraction line, the residence time forextracting the off-gas sample through the probe is markedly reduced.This extraction line which is periodically back purged to removeparticulate matter may also incorporate a suitably designed primaryfilter to further reduce fume infiltration. The extraction line may alsobe heated to maintain the off-gas temperature above the dew pointtemperature of the gas.

A hollow conduit also heated above the dew point temperature issubsequently used to continuously transfer the hot, wet off-gas samplefrom the probe to a nearby sampling station.

In the current system, the sampling station may be of novel design, andis preferably much more compact in size than the traditional analyzerunit associated with the conventional extractive method and has beendesigned to operate without the need for an environmentally protectiveroom. Because of the compact nature of the sampling station and theabsence of an associated environmentally controlled room, the samplingstation can be positioned directly on the plant floor in very closeproximity to the probe thereby further reducing response delaysassociated with transferring the off-gas.

The sampling station is configured to analyze gasses in two operationalsteps that greatly improve reliability and precision compared to the insitu optical method. First, the off-gas sample is cleaned of particulatematter with progressively finer filters. Second, the cleaned, wet gas isintroduced into a series of specially designed analytical cells witheach cell incorporating an optical transmitter connected by fiber opticcable to a remote tunable diode laser which generates a beam of thecorrect wavelength for the gas species being analyzed by said cell, and,an optical detector connected by coaxial cable to a remote signalanalysis unit. Unlike the fixed path length used to analyze all gaseousspecies in the in situ laser method, in the current method, the lengthof each analytical cell in the sampling station is tailored to theoptimum laser transmission length needed to meet the required analyticalprecision for the specific gas being analyzed in accordance with theanalytical requirements of the industrial application. Furthermore, thelaser used in the current method does not require regular calibrationchecks or calibration gases as with the current extractive method.

Filtering the off-gas to remove particulate prior to introducing theoff-gas sample into the analytical cells represents a major advancementover the current in situ method. The use of clean gas greatly reducesproblems associated with laser beam attenuation and interrupted signals.Furthermore, eliminating the laser attenuation problems allows thelength (L) of each analytical cell to be tailored to the optimum lasertransmission length needed to satisfy the analytical precisionrequirements for each gaseous species because there is no concern withlaser beam attenuation and scattering from particulate matter in theoff-gas sample.

Although not essential, most preferably the sampling station is providedwith a suitable heat source, such as quartz or resistance coil heater.The heat source is used to heat at least analyzing portions of thechamber interior to assist in maintaining the extracted gas sampletherein at a constant temperature, preferably the same as when initiallyextracted, as it moves through optical measuring cells.

The sampling station may be provided housed within a stand-alonecabinet, and which has a more compact in size compared to conventionalgas analyzer units associated with conventional extractive methods. Inone simplified design, a thermally divided cabinet having heated andunheated or cooled sections is provided. In a most preferredconstruction, the cabinet has both height and width dimensions less thanabout 150 cm, and preferably between about 50 to about 100 cm, and acabinet depth ranging from about 10 cm to about 50 cm.

Because of the compact nature of the sampling station cabinet and theabsence of an associated environmentally controlled room, the samplingstation can be positioned directly on the plant floor in closeproximity, and preferably within 1 to 50 metres, preferably within 2 to15, and more preferably within 5 to 10 metres to the probe. Thepositioning of the sampling station in such close proximityadvantageously reduces sample delivery distance, minimizing sampledegradation and response delays associated with the transfer of off-gassamples prior to analysis. Further, by locating the sampling station insuch proximity to the probe and gas extraction point, cooling and/orprecipitation of vapour and/or loss of volatile phases from wetextracted gas samples prior to analysis may be minimized.

The sampling station may further be provided with one or moreparticulate filters, wherein gas samples fed into the sampling stationare initially further cleaned of particulate matter. Most preferably, aseries of progressively finer filters provided upstream from the opticmeasuring cells through which the extracted off-gas sample passes as itis fed into and through prior to passing through or into one or moreoptical measuring cells for analysis.

In a preferred embodiment, the analytical cells are also designed tooperate at a temperature above the off-gas dew point thereby avoidingthe need for an additional off-gas condensation step. This eliminatesthe need for a condenser which further reduces the physical size of thesampling station. In addition, by analyzing wet off-gas, optimizing thedesign of each specific analytical cell and using proprietary softwarein the signal analysis unit, the current invention also enables fullspectrum analysis of H₂O vapor, CO, O₂, CO₂ and H₂. In manymetallurgical and combustion applications, having such a full spectrumanalysis enables the concentration N₂ to be determined by differencefrom 100%.

The current invention also enables a simplified and effectivearrangement for analyzing off-gas compositions at multiple sample pointsby connecting each sampling point's compact sampling station by fiberand coaxial cables to a common laser generator and signal analyzing unitequipped with a suitable multiplexer or splitter that distributes theoptical signals between the respective sampling stations.

In the current method, a multipoint optical analyzer is connected byfiber optic cables to the specially designed laser cells contained inthe sampling station which is located in close proximity to the probe.The optical analyzer is designed to contain multiple tunable diodelasers that generate laser beams in the desired wavelength rangespecific to each gaseous species being analyzed which may include but isnot limited to gases such as CO, CO₂, O₂ and H₂O vapor. Thecorresponding signals from these laser cells are electronically returnedto the remote optical analyzer for signal analysis to determine thegases composition. The sample station can also be designed to houseother analytical devices such as specially designed thermal conductivitycells and electrochemical cells as maybe required to provide additionalanalytical capabilities in tune with the needs of the industrialapplication. These additional sensors have been specially designed toanalyze wet off-gas by operating above the dew point temperature of thegas thereby eliminating the need for a condenser as required in theextractive technology. In addition, these sensors have been speciallydesigned to operate without the need for calibration gases.

As noted earlier, the optical analyzer is designed to have multipointanalytical capabilities and can analyze signals from up to but notlimited to 8 separate sampling stations which makes the current methodideally suited for industrial applications with multiple furnaces oroff-gas sampling points.

Although not essential, multiple sampling chambers are preferablyfluidically connected in series or in a parallel arrangement, and may beprovided as part of a modular unit which is removable andinterchangeable, allowing the sampling station to be easily tailoredspecifically to the specific desired off-gas components to be analyzed.Each cell sampling chamber is formed with a length (L) corresponding toa desired absorption profile of the target off-gas component to beanalyzed and includes an associated optical transmitter or emitter andan associated optical detector. With each sampling chamber, the length(L) between the optical transmitter and the associated detector istailored to the optimum emitted coherent light beam transmission lengthselected to meet the desired analytical precision for a chosen specificor target gas component to be analyzed, in accordance with theanalytical requirements of the individual industrial application. Thelasers used with the system do not require regular calibration checks orcalibration gases emitters of each measuring cell as with the existingextractive method. Rather the optical emitters in each cell areconnected by fiber optic cables to one or more remotely located tunablediode lasers. The lasers are operable to generate and emit from eachoptical transmitter a coherent light beam, and preferably a beam in themid-IR, near-IR and visible range of the correct wavelength for thespecific gas species being analyzed by the sampling chamber. Theassociated optical detectors in each sampling chamber are positioned toreceive and convert the collected emitted beam energy into data which istransmitted electronically by coaxial cable to a remote signal analysisunit and/or furnace control.

In addition the optical cell sampling chamber is designed to minimizethe internal volume so to reduce the gas resident time in the cell andthe associate delay.

In another embodiment, the measuring cell may be provided with one ormore sampling chambers adapted to receive a multiplexed laser beam. Themultiplexed beam comprising a collimated beam from multiple lasersources which is optically transmitted by way of a single fiber opticcable, and which upon detection by the cell is subsequentlyde-multiplexed for gas component analysis.

Accordingly, in a first aspect the present invention resides in anoff-gas analyzer apparatus for measuring gas components of a gas sampleto be analyzed, the apparatus comprising, a gas component measuring cellcomprising, first and second elongated sampling chambers, said samplingchambers being in fluid communication a gas inlet for receiving said gassample to be analyzed, said first and second sampling chambers extendingfrom a respective first end to a second end spaced therefrom, saidsampling chambers having a respective length correlated to an absorptionprofile of an associated target gas component of said gas sample to beanalyzed, an optical head being positioned towards the sampling chamberfirst ends, the optical head adapted for optical coupling to a coherentlight source and including a plurality of emitters, said emitters beingpositioned to emit a coherent light beam along an associated samplingchamber, a detector assembly being positioned towards the samplingchamber second ends, the detector assembly provided for electroniccoupling to a gas analyzer and including at least one detector forreceiving said coherent light beams emitted from said emitters, a filterassembly for filtering particulate matter from said gas sample prior toanalysis by said gas component measuring cell, and a gas conduitassembly substantially providing fluid communication between a gassample source and said filter assembly, and from said filter assemblyand said gas inlet.

In a second aspect, the present invention resides in an off-gas analysissystem for measuring gas components of a gas sample from a furnaceoff-gas stream, the system comprising, a gas analyzer apparatus, aprocessor, a coherent light source, and a gas conduit assembly forfluidically communicating said gas sample from a sampling point in saidoff-gas stream to said gas analyzer apparatus, the gas analyzerapparatus including, a gas component measuring cell comprising, a gasinlet fluidically communicating with said gas conduit assembly, aplurality of elongated sampling chambers, said sampling chambers beingin fluid communication the gas inlet for receiving said gas sampletherethrough, said sampling chambers extending from a respective end toa second end spaced therefrom, said sampling chamber having a respectivelength correlated to an absorption profile of an associated target gascomponent of said gas sample to be analyzed, an optical head beingposition towards the sampling chamber first ends, the optical headprovided for optical coupling to said coherent light source andincluding a plurality of emitters, said emitters being positioned toemit a coherent light beam substantially along as associated samplingchamber, a detector assembly electronically communicating with saidprocessor and including a plurality of optical detectors, said detectorsbeing positioned towards an associated sampling chamber second end fordetecting and converting non-absorbed portions of said associatedcoherent light beam as electric signals, a filter assembly in fluidcommunication with said conduit assembly and said gas componentmeasuring cell, the filter assembly disposed in an upstream positionfrom said gas inlet for filtering particulate matter from said gassample prior to analysis in said gas component measuring cell.

In a third aspect, the present invention resides in a furnace gasanalysis and control system comprising, at least one gas analyzerapparatus operable to measure selected gas components of an extractedfurnace off-gas sample, a system processor electronically communicatingwith each said gas analyzer and operable to output furnace controlsignals in response to the measured gas components detected thereby, acoherent light source, and a gas conduit assembly in fluid communicationbetween a selected sampling point in said off-gas stream and anassociated said gas analyzer apparatus, each said gas analyzer apparatusincluding, a gas component measuring cell comprising, a gas inlet andgas outlet, a plurality of elongated sampling chambers for receiving theextracted off-gas sample therein, said sampling chambers fluidicallycommunicating with each other and said gas inlet, the sampling chambersextending respectively from a first end to a second end spacedtherefrom, and having a respective length correlated to an absorptionprofile the selected gas component of said off-gas sample to beanalyzed, an optical head being positioned towards the sampling chamberfirst ends, the optical head provided for optical coupling to saidcoherent light source and including a plurality of emitters, saidemitters being positioned to emit a coherent light beam along anassociated sampling chamber, a detector assembly comprising an opticaldetector positioned towards each associated sampling chamber second endfor detecting and converting non-absorbed portions of said associatedcoherent light beam into electric signals, and a filter assemblydisposed in an upstream position from said gas inlet for filteringparticulate matter from said extracted off-gas sample prior to analysisin said gas component measuring, a pump assembly operable to convey saidoff-gas samples from said selected sampling points to the gas inlet ofselected said gas analyzer apparatus.

In addition to the foregoing, the present invention also provides fornumerous additional non-limiting aspects and which include:

An off-gas analyzer apparatus according to any of the preceding aspects,wherein said gas component measuring cell comprises first and secondremovable windows spaced towards and substantially sealing respectivelyeach of the first and second ends of the sampling chambers.

An off-gas analyzer apparatus according to any of the preceding aspects,wherein said emitters further comprise a collimator selected to emitsaid coherent light beam as a collimated light beam along saidassociated sampling chamber, and said detector assembly furthercomprises a lens associated with each said sampling chamber forrefocusing each said collimated light beam towards an associated saiddetector.

An off-gas analyzer apparatus according to any of the preceding aspects,wherein said first and second sampling chambers comprise generallyaxially aligned longitudinally extending cylindrical chambers, saidchambers being provided in fluidic communication along substantiallytheir entire longitudinal length, said gas inlet being fluidicallycoupled to said first sampling chamber adjacent to said first chamberfirst end, and a gas outlet being fluidically coupled to said secondsampling chamber adjacent to said second chamber second end.

An off-gas analyzer apparatus according to any of the preceding aspects,wherein said gas component measuring cell is provided as a modularremovable unit.

An off-gas analyzer apparatus according to any of the preceding aspects,further comprising a pump assembly operable to convey said gas samplefrom said gas sample source through said filter assembly and into saidmeasuring cell for analysis.

An off-gas analyzer apparatus according to any of the preceding aspects,wherein said off-gas analyzer comprises a cabinet, said gas componentmeasuring cell, said pump assembly and said filter assembly beingsubstantially housed within said cabinet.

An off-gas analyzer apparatus according to any of the preceding aspects,wherein said cabinet comprises a heated compartment, and a heaterassembly thermally communicating with said heated compartment, said gascomponent measuring cell being housed substantially within an interiorof said heated compartment, and wherein said heater assembly is operableto maintain said heated compartment interior at a temperature of betweenabout 105° C. and 130° C.

An off-gas analyzer apparatus according to any of the preceding aspects,wherein said coherent light source comprises a plurality of tunablediode lasers, said lasers being provided for optical coupling to anassociated emitter.

An off-gas analyzer apparatus according to any of the preceding aspects,wherein said gas sample comprises an off-gas sample from a steel makingfurnace off gas stream, and said target gas component is selected fromthe group consisting of N₂, CO, CO₂, H₂, water vapour, and O₂.

An off-gas analyzer apparatus according to any of the preceding aspects,wherein the cabinet further includes an unheated compartment, the pumpassembly including a pump motor being housed substantially within aninterior of the unheated compartment.

An off-gas analysis system according to any of the preceding aspects,wherein said gas conduit assembly includes an elongated sampling probefor extracting said off-gas sample from a generally central portion ofsaid furnace off-gas stream, and a heated conduit fluidically couplingsaid probe and said gas analyzer, the heated conduit operable to conveysaid extracted gas sample from said probe to said gas analyzer apparatusas a heated gas sample at a temperature selected at between about 80° C.and 150° C.

An off-gas analysis system according to any of the preceding aspects,wherein said gas component measuring cell comprises first and secondremovable windows spaced towards each of the first and second ends ofthe sampling chambers.

An off-gas analysis system according to any of the preceding aspects,wherein said emitters further comprise a collimator operable to emitsaid coherent light beam as a collimated light beam, and said detectorassembly further comprises a lens associated with each said samplingchamber, said lens configured to refocus the emitted collimated lightbeam towards the associated optical detector.

An off-gas analysis system according to any of the preceding aspects,wherein the plurality sampling chambers include first and secondgenerally cylindrical chambers, said first and second cylindricalchambers being provided in fluid communication along longitudinallyextending edge portions, said gas inlet being fluidically coupled tosaid first cylindrical chamber adjacent to said first chamber first end,and a gas outlet being fluidically coupled to said second cylindricalchamber adjacent to said second chamber second end.

An off-gas analysis apparatus or system according to any of thepreceding aspects, wherein said gas conduit assembly comprises a heatedgas conduit having a length selected at up to 50 metres, and preferablybetween about 2 and 15 metres.

An off-gas analysis system according to any of the preceding aspects,further comprising a pump assembly operable to convey said gas samplefrom said gas sample source through said filter assembly and into saidsampling chamber for analysis.

An off-gas analysis system according to any of the preceding aspects,wherein said gas analyzer apparatus further includes a cabinetcomprising a heated compartment, and a heater assembly thermallycommunicating with said heated compartment, said gas component measuringcell being housed substantially within an interior of said heatedcompartment, and wherein said heater assembly is operable to maintainsaid heated compartment interior at a temperature of between about 105°C. and 140° C.

An off-gas analysis system according to any of the preceding aspects,wherein the cabinet further includes an unheated compartment, the pumpassembly including a pump motor being housed substantially within aninterior of the unheated compartment.

An off-gas analysis system according to any of the preceding aspects,wherein said coherent light source comprises a plurality of tunablediode lasers, each said laser being provided for optical coupling to anassociated emitter.

An off-gas analysis system according to any of the preceding aspects,wherein said off-gas system comprises a steel making furnace off gasstream, and said gas components are selected from the group consistingof N₂, CO, CO₂, H₂, water vapour, and O₂.

A furnace gas analysis and control system according to any of thepreceding aspects, wherein the at least one gas analyzer apparatusincludes a first analyzer apparatus and a second analyzer apparatus, thecoherent light source comprises a plurality of tunable diode lasers, anda switching assembly is operable to selectively optically couple saidlasers and associated one of said emitters of a selected one of saidfirst and second analyzer apparatus.

A furnace gas analysis and control system according to any of thepreceding aspects, wherein said gas component measuring cell comprisesfirst and second removable windows spaced towards and substantiallysealing respectively each of the first and second ends of the samplingchambers, and each of the sampling chambers comprising a generallyco-axially aligned cylindrical chamber, the sampling chambers being influid communication along longitudinally extending adjacent edgeportions.

A furnace gas analysis and control system according to any of thepreceding aspects, wherein said emitters further comprise a collimatorselected to emit said coherent light beam as a collimated light beamalong said associated sampling chamber, and said detector assemblyfurther comprises a lens associated with each said sampling chamber forrefocusing each said collimated light beam towards an associated saiddetector.

A furnace gas analysis and control system according to any of thepreceding aspects, wherein said gas conduit assembly comprises anassociated heated gas conduit providing fluid communication between eachselected sampling point and each associated said gas analyzer apparatus,each associated heated gas conduit having a length selected at betweenabout 2 and 15 metres.

A furnace gas analyzer and/or analysis and control system according toany of the preceding aspects, wherein said gas component measuring cellis provided as a replaceable modular unit.

A furnace gas analysis and control system according to any of thepreceding aspects, wherein each gas analyzer apparatus is housedsubstantially within an associated cabinet, each said cabinet comprisesa heated compartment, and a heater assembly thermally communicating withsaid heated compartment, said gas component measuring cell being housedsubstantially within an interior of said heated compartment, saidcabinet having width, length and height dimensions each selected atbetween about 0.1 and 2 metres.

A furnace gas analysis and control system according to any of thepreceding aspects, comprising a plurality of said gas analyzerapparatus, and wherein said furnace comprises a steel making furnace,and said selected gas component is selected from the group consisting ofN₂, CO, CO₂, H₂, water vapour, and O₂.

A furnace gas analysis and control system according to any of thepreceding aspects, wherein each said gas analyzer apparatus furtherincludes a water vapour sensor fluidically communication with said gascomponent measuring cell for sensing water vapour concentration in saidsample.

A furnace gas analysis and control system according to any of thepreceding aspects, wherein said water vapour sensor is disposed in saidheated compartment of said cabinet.

Use of a furnace gas analysis and control system according to anypreceding aspect, or comprising a plurality of the off-gas analyzerapparatus according to any preceding aspects, at least one coherentlight source for optically communicating coherent light to the off-gasanalyzer apparatus, and a system processor electronically communicatingwith each said off-gas analyzer apparatus and the at least one coherentlight source, wherein, the gas conduit assembly of a first said off-gasanalyzer being provided in fluid communication with a first samplinglocation along a furnace off-gas fume duct for receiving associatedextracted gas samples therefrom, and the gas conduit assembly of asecond said off-gas analyzer being provided in fluid communication witha second sampling location along the furnace off-gas fume duct forreceiving associated extracted gas samples therefrom, and wherein saidsecond sampling station is spaced from said first sampling station, andwherein in use, following the extraction and communication of theassociated extracted gas sample, into the sampling chambers of the firstgas analyzer, with said system processor, actuating said first off-gasanalyzer to emit coherent light beams from at least one said coherentlight source along the sampling chambers, and by the detector assembly,detecting and measuring the emitted coherent light beams in the samplingchambers as an absorption profile of an associated target off-gascomponent selected from the group consisting of N₂, CO, CO₂, H₂, O₂ andwater vapour at said first sampling locations, and following theextraction and communication of the associated extracted gas samples tothe sampling chambers of the second gas analyzer, with the systemprocessor, actuating said second off-gas analyzer to emit coherent lightbeams from at least one said coherent light source along the samplingchambers, and by the detector assembly, detecting and measuring theemitted coherent light beams as an absorption profile of the associatedtarget off-gas component at said second sampling location, and comparingthe measured absorption profiles of the target off-gas components andthe first and second sampling locations, and generating furnace controlsignals based on the comparison.

Use of the furnace gas analysis and control system according to any ofthe preceding aspects wherein the system processor is operable topreferentially actuate one or more of said off-gas analyzers byincreased time and/or frequency to effect a gas sample analysis which isweighted to one or more sampling locations along the furnace off-gasfume duct.

Use of the furnace gas analysis and control system according to any ofthe preceding aspects further wherein during actuation of the firstoff-gas analyzer, maintaining a temperature in the sampling chambersabove a dew point of the associated extracted gas sample, and wherein atleast one associated target off-gas component comprises water vapour.

Use of the furnace analysis and control system according to any of thepreceding aspects wherein the furnace gas analysis and control systemfurther includes an optical switching assembly operable to selectivelyoptically couple at least one said coherent light source and the opticalhead of the first off-gas analyzer and/or the second off-gas analyzer,the system processor being operable to selectively actuate a selectedone of the first and second off-gas analyzer apparatus, and operatingthe optical switching assembly to optically couple the at least onecoherent light source to each of the first and second off-gas analyzerwhen selectively actuated.

Use of the furnace gas analysis and control system according to any ofthe preceding aspects wherein said coherent light source comprises atunable diode laser.

Advantages of the Current Invention

The applicant has appreciated that various preferred features of thecurrent invention may combine to achieve one or more non-limitingadvantages and which may include:

-   -   Analytical Capabilities: Unlike in situ laser systems that        provide only a partial off-gas analysis, the current invention        may incorporate laser cells together with other analytical        devices as required into a sampling station which are operable        to analyze full or more complete spectrum off-gas chemistry. For        example, in steelmaking furnace applications, the current        invention is preferably designed to analyze 5 gaseous species        CO, CO₂, O₂, H₂ and H₂O vapor, and thereby may be operable to        determine N₂ concentration by difference analysis, as explained        previously.    -   Analytical Precision: Unlike in situ laser systems that use a        fixed path length to analyze all gaseous species with said fixed        path length determined as a compromise between analytical        precision and minimized laser beam attenuation problems, in a        preferred aspect the current invention may incorporate        individual laser measuring cells which may be tailored for the        sampling for each gaseous species being analyzed. Preferably,        individual laser cells are tailor designed to provide the        optimum laser transmission length needed to satisfy the        analytical precision requirements for each gaseous species.    -   Calibration: Unlike extractive systems which require routine        calibration checks and expensive specialized calibration gases,        the use of laser measuring cells and other analytical devices        may avoid the requirement of manual calibration checks or        specialized calibration gases.    -   Analytical Response Delay: Unlike extractive systems which have        lengthy response times often of the order of 20 to 40 seconds,        the current system advantageously may utilize a high velocity        pump to extract the off-gas sample at relatively higher flow        rates, and/or through probes, which in the preferred embodiment        incorporate a centrally located, smaller diameter extraction        line. Apertures into the extraction line may be extended        downwards to be in close proximity to the opening of the main        body larger diameter probe. Off-gases may be directed at high        velocity to a small sized sampling station that can be        positioned directly on the shop floor and without the need for        protective room, removing space considerations that hinder the        positioning of conventional sampling stations in close proximity        to the probe. Unlike extractive analyzers which use only a small        fraction of the gas flow extracted from a slip stream, the laser        measuring cells and other analytical devices located inside the        sampling station are preferably designed to facilitate the high        flow off-gas at rates of nominally but not necessarily up to 40        liters per minute, reducing the analytical response delay of the        current invention to about 8 seconds or less.    -   Analytical Reliability: Unlike the in situ laser systems that        rely on passive transmission of laser beam(s) through the        off-gas fume from an emitter to a detector and can suffer from        attenuation of the laser beam that prevents a sufficient level        of detection resulting in interrupted off-gas analysis, the        current invention has very high analytical reliability which may        be equivalent or better than the extractive systems. The current        invention is “active” technology that uses forced extraction        that ensures a sample of off-gas is delivered to the analytical        measuring cells. Unlike in situ laser methods, reliability of        laser beam transmission is enhanced by first filtering the        off-gas sample through a series of filters selected to remove        particulate matter before introducing the filtered gases into        the laser measuring cells.    -   The current method is interfaced with the furnace control        network so that whenever the industrial process is producing        off-gas, the current invention automatically switches on a pump        to provide high suction to actively extract a sample of off-gas        through the probe, and deliver it at high velocity to the        sampling station for filtration and analysis. When the        industrial process is in standby mode and not producing off-gas,        the current system may operate to automatically switch to a        filter and probe back purge to remove any accumulated        particulate matter.    -   Installation and Maintenance Considerations: Extractive systems        have higher installation costs and require more maintenance than        in situ systems. The current invention allows for the use of a        more compact sampling station that can be located directly on        the shop floor, avoiding the installation costs and complexities        of installing a large analyzer in an environmentally protective        enclosure. The current method also allows for analysis of        filtered wet, hot gases, and thereby may avoid the maintenance        required to service a water vapor condenser. In addition the        current invention minimizes the need for manual calibration        checks or specialized calibration gases.    -   Process Control Functionality: Unlike the in situ laser method        which cannot provide a full spectrum off-gas chemistry, in a        preferred aspect, the invention is designed to provide full        spectrum off-gas analysis, including but not limited to CO, CO₂,        O₂, H₂ and H₂O vapor.    -   For example, the following table provides the analytical        capabilities of the various off-gas analysis technologies        together with the key gaseous species analyses required to        provide complete process control and optimization functionality        in a steelmaking furnace. As shown, most preferably the current        system provides a full spectrum off-gas analysis, including the        analysis of N₂ by difference, without many of the disadvantages        of conventional extractive technology. The current invention may        thus provide a more complete off-gas analysis spectrum having        the advantage over the limited analytical capability provided by        in situ laser technology, and which is not technically capable        of analyzing many mononuclear diatomic gases including N₂ and H₂        (S. Schilt, F. K. Tittel and K. P. Petrov, “Diode Laser        Spectroscopic Monitoring of Trace Gases”, Encyclopedia of        Analytical Chemistry, pages 1-29, 2011).

Off-Gas Analysis Method Off-Gas Species Analytical Capabilities CO CO₂O₂ H₂ H₂O N₂ Current System

Extractive Systems

In situ Laser System - equipped

with 1 laser In situ Laser System - with

2 lasers In situ Laser System - with

3 lasers Steelmaking Process Function Process is oxidizing or reducing

Gas burner firing control &

optimization Carbon combustion control &

optimization Oxygen lancing control &

optimization Fume system suction to control air

ingress Water leak detection

Close a real-time Mass & Energy

Balance

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the following detailed description takentogether with accompanying drawings in which:

FIG. 1 illustrates schematically a furnace gas analysis and controlsystem in accordance with a preferred embodiment of the invention;

FIG. 2 illustrates schematically a gas extraction probe used in theanalysis and control system of FIG. 1;

FIG. 3 illustrates schematically a gas sampling analyzer used in the gasanalysis and control system of FIG. 1;

FIG. 4 illustrates schematically an interior view of the gas samplinganalyzer shown in FIG. 3, illustrating gas water vapour and gascomponent measuring cells and a gas filter assembly in accordance with apreferred embodiment;

FIG. 5 shows an enlarged perspective view of the gas component measuringcell shown in FIG. 4;

FIG. 6 illustrates schematically the gas component measuring cell shownin FIG. 5; and

FIG. 7 shows a cross-sectional view of the gas component measuring cellillustrated in FIG. 6 taken along line 7-7′.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference may be had to FIG. 1 which illustrates a furnace gas analysisand control system 10 used in the off-gas analysis and control of anindustrial steel making furnace, in accordance with a preferredembodiment of the invention. As shown best in FIG. 1, the system 10includes three gas sampling analyzers 12 a,12 b,12 c which are opticallyand electronically connected to a control unit 20, by way of a suitablebi-strand fiber optic/coaxial cable 30. Each of the sampling analyzers12 a,12 b,12 c are further provided in gaseous communication with afurnace gas fume duct 16 by an associated gas extraction conduitassembly 14 a,14 b,14 c.

As illustrated, each conduit assembly 14 a,14 b,14 c is provided with agas extraction probe 18 a 18 b,18 c positioned at a respectivepre-selected off-gas extraction sampling point A,B,C provided atlongitudinally spaced locations along the furnace fume duct 16.

The system control unit 20 may be provided in a location remote from thesampling analyzers 12 a,12 b,12 c, and preferably at a location isolatedfrom both high furnace temperatures and dust. The control unit 20includes a processor 22 such as a CPU, three tunable diode lasers (TDLs)24 a,24 b,24 c which are operable to output a coherent light beam in themid-IR range, an optical switching unit 26, a programmable logiccontroller (PLC) 28, and a multiplexer/de-multiplexer 32.

As will be described, the optical switching unit 26, in conjunction withthe multiplexer/de-multiplexer 32 and fibre optic/coaxial cables 30 isused to selectively optically and electronically couple the lasers 24a,24 b,24 c to each gas sampling analyzer 12 a,12 b,12 c, depending onthe desired sampling point A,B,C, from which an off-gas sample is to beextracted and analyzed. Most preferably, the fiber optic/coaxial cables30 are provided with a secondary coaxial conduit used to transmitelectron signals from the gas sample analyzers 12 a,12 b,12 c to logiccontroller and CPU 22 for control of both the switching unit 26, anddepending on the data received, furnace plant operational control. Whilethe use of a multiplexer/de-multiplexer 32 advantageously permits lasers24 a,24 b,24 c to be optically connected to separate analyzers 12 a,12b,12 c, in an alternative construction, one or more optical splitterscould be used to allow output laser beam energy to be split andseparately simultaneously transmitted to multiple analyzers 12 a,12 band/or 12 c at lower power levels.

In one possible mode of operation, the gas extraction probes 18 a,18b,18 c are positioned along the fume duct 16 at preselected extractionpoints A,B,C which are prioritized in relation to the importance of theselected gas component analysis to be performed by each associatedsampling analyzer 12 a,12 b,12 c, in assessing overall furnaceoperational performance. In operation, the control unit processor 22 isused to selectively activate and control each gas sampling analyzer 12a,12 b,12 c to extract an off-gas sample by way of the associated probe18 a,18 b,18 c, and analyze one or more target gas components therein atthe selected extraction points A,B,C. It is envisioned that in apreferred mode of operation, the processor 22 may be used to effect theweighted gas sample extraction and analysis either more frequentlyand/or for longer periods of time at the critically most important gassampling point A, than as compared with the extraction and analysisperformed at secondary sampling points B and C. In this manner, in onepossible mode of operation, the processor 22 may be used to activate thesampling analyzers 12 a,12 b,12 c so as to effect weighted sampleextraction and analysis from the individual sampling points in the orderA,B,A,C,A,B,A,C. It is to be appreciated that in an alternate mode ofoperation, each of the sampling analyzers 12 a,12 b,12 c could merely beoperated sequentially to effect cyclical extraction and analysis atsampling points A,B,C,A,B,C,A,B,C in a sequenced mode of operation;and/or extraction and analysis may be performed at selected samplingpoint A for longer periods of time than is performed at sampling pointsB or C.

Each gas conduit assembly 14 a,14 b,14 c is shown as including, inaddition to the extraction probes 18 a,18 b,18 c, a sample gas supplyconduit 34 and a purging gas return line 36. FIG. 2 illustrates best theextraction probe 18 used in each gas conduit assembly 14 a,14 b,14 cshown in FIG. 1. Preferably, the probe 18 is an elongated hollow tubularwater cooled probe having open end 37 provided for positioning insidethe fume duct 16 at the desired sampling point in the exhaust gas flow100. To minimize the delay time associated with extracting the off-gassample through the probe 18, the probe 18 incorporates a coaxiallylocated smaller diameter extraction line 38. As shown best in FIG. 2,the end of the extraction line 38 extends downwardly along the probeinterior, to be in close proximity to the end opening 37 of the mainlarger diameter body of the probe 18. By using the extended smallerdiameter extraction line 38, the residence time for off-gas sampleextracted through the probe 18 is markedly reduced. The end of theextraction line 38 may also incorporate a suitably designed primaryfilter, to reduce any fume dust infiltration therein. The extractionline 38 is preferably cleaned by periodically back purging, as forexample, by selectively supplying a pressurized nitrogen gas or reverseairflow through the extraction line 38 from a suitable pressurizedsource or pump assembly 64 (FIG. 4), via the gas return conduit 36 todislodge and remove particulate matter accumulated thereon.

In an alternate construction, the gas return conduit 36 may be providedto exhaust analyzed sample gas back into the fume duct 16, and/orprovide the pressurized purging gas flow along the interior of the probe18, to facilitate cleaning and the dislodging of any dust or debrisaccumulating along the outside of the extraction line 38.

FIG. 2 illustrates the extraction line 38 of each probe 18 as beingfluidically coupled to the gas supply conduit 34, used to conveyextracted off-gas samples from each sampling point A,B,C to theassociated gas sampling analyzer 12 a,12 b,12 c. The gas supply conduit34 is shown as fluidically coupled to the upper outer end of the probeextraction line 38 to receive the extracted gas sample therefrom. Thesupply conduit 34 is provided with a resistance coil heater strip orother suitable heating jacket 40 and surrounding thermal insulation 41.The heater strip 40 is operable to maintain the extracted gas sample ata temperature of between about 80° C. and 160° C., and more preferably100° C. to 130° C.±10° C. as the sample moves along the gas supplyconduit 34 between the probe 18 and to the associated gas samplinganalyzer 12.

FIGS. 3 and 4 show best each gas sampling analyzer 12 used in the system10 in accordance with a preferred embodiment of the invention. Thesampling analyzer 12 is provided with an exterior metal cabinet 44 whichis divided internally into heated and cooled or cold sections 46,48. Thecabinet 44 is provided with an overall compact design having width andheight dimensions of between about 0.5 to 1.25 metres, and a cabinetdepth of about 0.15 to 0.4 metres. The compact size of the gas analyzer12 advantageously allows its placement in closer proximity to the fumeduct 16, and without the requirement that it be housed with a dedicatedor special room or enclosure. As a result, the gas sampling analyzers 12a,12 b,12 c may be provided in close proximity to, and preferably within1 to 20 metres, and most preferably within 5 to 15 metres of theassociated sampling point A,B,C, with a corresponding shorter length ofgas sampling conduit 34 being used to communicate with each probe 18a,18 b,18 c.

As illustrated schematically in FIG. 3, the heated section 46 of thecabinet 44 is used to house a gas filter assembly 50, a gas componentoptical measuring cell 60 used to detect and measure selected target gascomponents in the extracted off-gas sample, and a water detection cell52 for detecting water vapour content in the extracted gas.

An induction coil heater 54 (FIG. 4) is disposed within the heatedsection 46 of the cabinet 44. The heater 54 is operable to heat theheated section 46 to a temperature above the condensation point of watervapour in the extracted off-gas sample, preferably to a temperaturebetween about 80° C. and 160° C., and more preferably from about 100° C.to about 130° C.±10° C. As will be described, preferably, the gascomponent measuring cell 60 is operable to measure the concentration ofCO, CO₂, O₂ and/or H₂ as individual components of the extracted off-gassample. FIG. 3 illustrates schematically the cold section 48 of thecabinet 44 as housing the pump motor 66 of the gas analyzer pumpassembly 64 (FIG. 4), as well as general cooling and purging valves,temperature sensors 70 and the gas analyzer electronics 72 which may bemore susceptible to temperature damage.

FIG. 4 illustrates best the pump assembly 64 as further having a pumphead 74 which is mechanically operable by way of the pump motor 66. Thepump head 74 is positioned within the heated section 46 of the cabinet44. It is to be appreciated that by maintaining the pump motor 66 in thecooled section 48, the risk of pump overheating and damage may beminimized.

FIG. 4 illustrates the heated gas supply conduit 34 as fluidicallycommunicating with internal cabinet gas supply conduit 120 disposedwithin the cabinet heated section 46, and which is fluidically coupledto the pump head 74. Because the heated section 46 is maintained at adesired heated temperature by the induction coil heater 54, separateheating for the gas supply conduit 120 as it extends through the cabinet44 is not required.

The filter assembly 50 includes an upstream coarse particulate filter 52a and a downstream fine particulate filter 52 b. The gas supply conduit120 is provided to convey the extracted gas sample initially through tothe measuring cell 60 after it passages through the coarse filter 52 a,pump head 74 and the fine filter 52 b. The applicant has appreciatedthat by providing the pump head 74 upstream from the fine filter 52 aand in a position downstream from the coarse filter 52 a, the extractedgas sample is advantageously introduced into the fine filter 52 b undera positive pressure. FIG. 4 further illustrates the conduit 120 asfluidically communicating with both the measuring cell 60 and watervapour sensor 62 for detecting sample water vapour content upstreamthereof. It is to be appreciated, that in an alternate embodiment, theoptical measuring cell 60 could be positioned upstream from the watervapour sensor 62, and/or the water vapour sensor 62 could be omittedfrom the gas analyzer 12 in its entirety.

As a result, the activation of the pump assembly 64 is used to extractand draw off-gas samples through the probe 18 and along the heated gassupply tube 34 into the cabinet 44. As the gas sample moves into thecabinet 44 it moves via conduit 120 through the filters 52 a,52 b, andthen into the water vapour sensor 62 and optical measuring cell 60.

FIGS. 5 to 7 illustrate best the gas component measuring cell 60 used inthe gas sampling analyzer 12 shown in FIG. 4. Most preferably, themeasuring cell 60 is provided as a modular unit which is adapted forsimplified replacement and removal. The measuring cell 60 is shown bestin FIGS. 6 and 7 as including two elongated and parallel arrangedcylindrical sampling chambers 80 a,80 b. Each of the sampling chambers80 a,80 b extend along parallel longitudinal axis from adjacent firstends 84 to respective second ends 88 spaced therefrom. As shown best inFIG. 7, the sampling chambers 80 a,80 b are open to each other by anarrow slit opening 89 extending along their proximate longitudinaladjacent edges, and which has a width selected to allow substantiallyunrestricted gas flow therebetween, whilst substantially preventing themovement of light energy from the sampling chamber 80 a into chamber 80b and vice versa.

FIG. 6 illustrates the measuring cell 60 as further including a gasinlet port 82 open to the sampling chamber 80 a adjacent to its firstend 84, with a gas outlet port 86 open to sampling chamber 80 b adjacentto its second opposed end 88. The lengths of each of the samplingchambers 80 a,80 b is correlated to an absorption profile of the desiredtarget gas component to be analyzed by the measuring cell 60. Further,by its modular nature, each cell 60 may be readily replaced and theanalyzer 12 modified to detect different gas components by selectingsampling chambers 80 a,80 b having the desired target gas absorptionprofiles.

FIG. 5 illustrates the measuring cell 60 as including an optical head 90positioned towards the first ends 84 of the chambers 80 a,80 b. Theoptical head 90 is provided with a pair of optical emitters 92 a,92 beach respectively coaxially aligned with the sample chamber 80 a,80 blongitudinal axis. Most preferably each of the emitters are providedwith a collimator. The optical emitters 92 a,92 b are opticallyconnected by way of the fibre optical cabling of the fiber optic/coaxialcables 30 to the tunable diode lasers 24 a,24 b by way of the switchingunit 26. Each optical emitter 92 a,92 b further includes a collimator94, adapted to broaden the width of the laser beam emitted therefrom, soas to minimize any potential interference by dust or particles which maybe entrained in the extracted off-gas sample. In this manner thecoherent light beam from the lasers 24 a,24 b is emitted from eachrespective emitter 92 a,92 b as a collimated laser beam, therebyreducing the potential that remaining entrained dust or particulatematter is the gas sample could result in false readings.

Preferably, a removable window or lens 96 is positioned at the firstends 84 of the chambers 80 a,80 b. When positioned, the window 96substantially seals the first ends 84 of the sampling chambers 80 a,80 bpreventing the movement of sampled gas and/or any entrained dusttherepast. A removable window or lens 104 further is provided at thesecond end 88 of the sampling chambers 80 a,80 b to seal the samplingchamber second ends 88. The removal of the windows 96,104 advantageouslyallows for simplified cell maintenance and periodic cleaning.

FIG. 6 further illustrates the measuring cell 60 as having a detectorassembly 98 positioned toward the second end 88 of the sampling chambers80 a,80 b. The detector assembly 98 includes a pair focusing lenses 102a,102 b and optical detectors 106 a,106 b positioned towards the secondends 88 of each respective sampling chamber 80 a,80 b. The opticalsensor 106 a,106 b are provided in electronic communication with the CPU20 by way of coaxial wiring of the fiber optic/coaxial cable 30. Thefocusing lenses 102 a,102 b are selected to refocus the collimated laserbeams towards each respective detector 106 a,106 b with the light energycollected thereby converted to electronic data signals.

For water vapour analysis, the extracted gas sample is passed throughthe water vapour sensor 62 prior to analysis in the measuring cell 60.In one non-limiting construction, the sensor 62 may be an opticallybased sensor constructed in a manner similar to measuring cell 60. Insuch a construction, the sensor 62 may be provided for selective opticalcoupling to laser 24 c by way of fiber optic cabling of fiberoptic/coaxial cable 30. Most preferably the water vapour sensor 62 isprovided with a coherent light source emitter which is optically coupledto the laser 24 c, and detector. The sensor 62 is provided with anoptical length which corresponds to an absorption profile for watervapour in the selected gas sample.

In use of the gas analysis and control system 10, the CPU 20 is used toactivate the selected gas sampling analyzer 12 a,12 b,12 c to extractand analyze an off-gas sample at the desired extraction point A,B,C ofinterest. Signals from the CPU 20 are received by the selected analyzerelectronics 72, and used to activate its pump motor 66. As the motor 66is activated, the off-gas sample is substantially continuously drawnfrom the fume duct 16 and along the gas supply conduits 34 viaassociated extraction probe 18 into the heated section 46 of the cabinet44. Most preferably, the pump motor 66 is selected to convey theextracted gas sample along the supply conduit 34 and through the filter52 a and measuring cell 60 at higher flow rates, as for example of up toabout 40 litres per minute, to minimize residence time and analyticalresponse delays. As the extracted gas sample moves through the cabinet44, it passes via conduit 120 through the coarse filter 52 a. Theoff-gas sample is then forced under positive pressure through the finefilter 52 b, and into the water sensor 62 for water content analysis. Onmoving from the water sensor 62, the off-gas sample moves and via thegas inlet port 82, into the sampling chambers 80 a,80 b of the measuringcell 60.

Concurrently, the control unit 20 is used to emit coherent light beamsfrom the lasers 24 a,24 b,24 c from the optical emitters 92 a,92 b ofthe measuring cell 60 as well as from an emitter within the water vapoursensor 62, for detection by the associated detectors.

In the optical measuring cell 60, each sampling chamber 80 a,80 b isprovided with a longitudinal length which is correlated to an absorptionprofile of the specific target gas component which is to be analyzed. Ina most preferred construction, the sample chambers 80 a,80 b areprovided with lengths correlating to absorption profiles selected foranalyzing respectively CO and CO₂, and O₂ concentrations in theextracted off-gas sample. The coherent light beams emitted by theoptical emitters 92 a,92 b are focused and are detected by the opticaldetectors 106 a,106 b respectively. The detector and analyzerelectronics 72 convert the detected light energy to electronic datasignals, which are thereafter transmitted by way of the coaxial cablingof fiber optic/coaxial cables 30 back to the CPU 20. Depending upon theconcentration and/or change of selected target components in the sampledoff-gas, the control unit 20 may thereafter output control signals tothe furnace plant to regulate or vary overall furnace operations.

It is to be appreciated, in a preferred construction a single laser maythus be used to effect both CO and CO₂ analysis. In an alternateembodiment, separate sample chambers 80 could however be provided toindividually analyze CO and CO₂ and which could be optically coupled toseparate or a common coherent light source.

In the preferred embodiment, the gas analyzer cell 60 is also designedto operate at temperatures above the off-gas dew point and/orcondensation point of vapour and/or validate phase gas components. Thisadvantageously avoids the need for an additional off-gas condensationstep, and the need for a condenser, allowing for a further reduction inthe physical size of the sampling station. In addition, by analyzing wetoff-gas and optimizing the design of each specific analytical cell andusing suitable software in the signal analysis unit, the currentinvention also enables full spectrum analysis of a variety of differenttypes of gases including, without restrictions H₂O vapor, CO, O₂, CO₂and H₂. In many metallurgical and combustion applications, having such afull spectrum analysis enables the concentration N₂ to be determined bydifference from 100%.

Following analysis, the analyzed gas sample is then vented either intothe atmosphere, or optionally, vented back into the fume duct 16 by wayof the gas return conduit 36. While the use of a gas return conduit 36to return sampled gas to the fume duct 16 may represent one embodimentof the invention, the invention is not so limited. In alternateconfiguration, the gas return conduit 36 may be used to convey purgingnitrogen gas to the extraction probe 18 to assist in probe cleaning.Valving within the cooled section 48 of the cabinet 44 may be providedto control and facilitate purging operations.

The current invention also enables a simplified and effectivearrangement for analyzing off-gas compositions at multiple sample pointsA,B,C by connecting a compact sampling analyzer 12 at each samplingpoint by fiber optic/coaxial cables 30 to common lasers 24 and a singleCPU 20 or signal analyzing unit equipped to distribute the opticalsignals between the respective sampling stations 12.

While the detailed description describes the apparatus 10 as includingtunable diode lasers 24 a,24 b,24 c, which are operable in the mid-IRrange it is to be appreciated that other lasers and/or optical analyzersmay also be used. Other types of lasers which could be selected includethose which are operable in the near-IR and visible wavelength range.Similarly whilst the aforementioned description describes the system 10as being used in the analysis of dusty industrial steel plant furnaceoff-gases, it is to be appreciated that the current system and methodhas application across a variety of different types of exhaust systems.These include other types of industrial furnaces, as well as coal andpower generated off-gas flue streams and the like.

Although the detailed description describes the control system 10 asincluding three sampling cabinets 12 a,12 b,12 c, it is to beappreciated that the system 10 may be installed with fewer or greaternumber of sampling cabinets 12 without departing from the presentinvention. Similarly, while the invention shown in FIG. 1 illustratesthe system 10 as including a gas extraction probe 18 a,18 b,18 cassociated with each gas sampling cabinet 12 a,12 b,12 c, in analternate configuration, the number of extraction probes 18 could beprovided for selective fluid communication with a single samplingcabinet 12 with a view to minimizing system hardware costs.

While the detailed description describes each sampling analyzer 12 ashaving a single measuring cell 60 which includes two parallel samplingchambers 80 a,80 b, the invention is not so limited. It is to beappreciated that the gas sampling analyzers 12 may include multiplemeasuring cells 60, each with fewer or greater numbers of samplingchambers 80 provided for optical and electric coupling to associatedcoherent light source emitters and detectors. Similarly, while thepreferred measuring cell 60 is described as having generally cylindricalsampling chambers 80 which fluidically communicate by way of alongitudinal slit opening, the invention is not restricted specificallyto the best mode which is described. Sampling chambers having differinglengths and/or profiles may also be used and will now become apparent.

The system 10 is described with reference to FIG. 1 whereby separatelasers 24 a,24 b are used to emit coherent light beams along arespective sample chamber 80 a,80 b for CO, CO₂ and O₂ analysis. In analternate construction, a single laser source could be provided tomeasure each of CO, CO₂ and O₂ with output beam energy either splitbetween sampling chambers 80 a,80 b by a suitable optical splitter (notshown), or switched therebetween by a multiplexer 28 and/or switchingunit 26.

Although the detailed description describes and illustrates variouspreferred embodiments, the invention is not restricted to the specificconstructions which are described. Many variations and modificationswill now occur to persons skilled in the art. For a definition of theinvention, reference may now be had to the appended claims.

We claim:
 1. An off-gas analyzer apparatus for measuring gas componentsof a gas sample to be analyzed, the apparatus comprising, a gascomponent measuring cell comprising, first and second elongated samplingchambers, said sampling chambers being in fluid communication with a gasinlet for receiving said gas sample to be analyzed, said first andsecond sampling chambers extending from a respective first end to asecond end spaced therefrom, said sampling chambers having a respectivelength correlated to an absorption profile of an associated target gascomponent of said gas sample to be analyzed, an optical head beingpositioned towards the sampling chamber first ends, the optical headadapted for optical coupling to a coherent light source and including aplurality of emitters, said emitters being positioned to emit a coherentlight beam along an associated sampling chamber, a detector assemblybeing positioned towards the sampling chamber second ends, the detectorassembly provided for electronic coupling to a gas analyzer andincluding at least one detector for receiving said coherent light beamsemitted from said emitters, a filter assembly for filtering particulatematter from said gas sample prior to analysis by said gas componentmeasuring cell, and a gas conduit assembly substantially providing fluidcommunication between a gas sample source and said filter assembly, andfrom said filter assembly and said gas inlet.
 2. The apparatus of claim1, wherein said gas component measuring cell comprises first and secondremovable windows spaced towards and substantially sealing respectivelyeach of the first and second ends of the sampling chambers.
 3. Theapparatus as claimed in claim 1 or claim 2, wherein said emittersfurther comprise a collimator selected to emit said coherent light beamas a collimated light beam along said associated sampling chamber, andsaid detector assembly further comprises a lens associated with eachsaid sampling chamber for refocusing each said collimated light beamtowards an associated said detector.
 4. The apparatus as claimed in anyone of claims 1 to 3, wherein said first and second sampling chamberscomprise generally axially aligned longitudinally extending cylindricalchambers, said chambers being provided in fluidic communication alongsubstantially their entire longitudinal length, said gas inlet beingfluidically coupled to said first sampling chamber adjacent to saidfirst chamber first end, and a gas outlet being fluidically coupled tosaid second sampling chamber adjacent to said second chamber second end.5. The apparatus as claimed in any one of claims 1 to 4, wherein saidgas conduit assembly comprises a heated gas conduit having a lengthselected at between about 2 and 15 metres.
 6. The apparatus as claimedin any one of claims 1 to 5, wherein said gas component measuring cellis provided as a modular removable unit.
 7. The apparatus as claimed inany one of claims 1 to 6 further comprising a pump assembly operable toconvey said gas sample from said gas sample source through said filterassembly and into said measuring cell for analysis.
 8. The apparatus asclaims in claim 7, wherein said off-gas analyzer comprises a cabinet,said gas component measuring cell, said pump assembly and said filterassembly being substantially housed within said cabinet, said pumpassembly and said sampling chambers being selected whereby said gassample is received in said measuring cell as a high velocity sample flowhaving a flow rate selected at between about 10 to 40 litres per minute.9. The apparatus as claimed in claim 8, wherein said cabinet comprises aheated compartment, and a heater assembly thermally communicating withsaid heated compartment, said gas component measuring cell being housedsubstantially within an interior of said heated compartment, and whereinsaid heater assembly is operable to maintain said heated compartmentinterior at a temperature of between about 105° C. and 130° C.
 10. Theapparatus as claimed in any one of claims 1 to 9, wherein said coherentlight source comprises a plurality of tunable lasers, at least one saidlaser being provided for optical coupling to at least one associatedemitter.
 11. The apparatus as claimed in any one of claims 1 to 10,wherein said gas sample comprises an off-gas sample from a steel makingfurnace off gas stream, and said target gas component is selected fromthe group consisting of CO, CO₂, H₂, water vapour, and O₂.
 12. Theapparatus as claimed in claim 8 or claim 9, wherein the cabinet furtherincludes an unheated compartment, the pump assembly including a pumpmotor being housed substantially within an interior of the unheatedcompartment.
 13. An off-gas analysis system for measuring gas componentsof a gas sample from a furnace off-gas stream, the system comprising, agas analyzer apparatus, a processor, a coherent light source, and a gasconduit assembly for fluidically communicating said gas sample from asampling point in said off-gas stream to said gas analyzer apparatus,the gas analyzer apparatus including, a gas component measuring cellcomprising, a gas inlet fluidically communicating with said gas conduitassembly, a plurality of elongated sampling chambers, said samplingchambers being in fluid communication the gas inlet for receiving saidgas sample therethrough, said sampling chambers extending from arespective end to a second end spaced therefrom, said sampling chamberhaving a respective length correlated to an absorption profile of anassociated target gas component of said gas sample to be analyzed, anoptical head being position towards the sampling chamber first ends, theoptical head provided for optical coupling to said coherent light sourceand including a plurality of emitters, said emitters being positioned toemit coherent light beam energy substantially along as associatedsampling chamber, a detector assembly electronically communicating withsaid processor and including a plurality of optical detectors, saiddetectors being positioned towards an associated sampling chamber secondend for detecting and converting non-absorbed portions of saidassociated coherent light beam as electric signals, a filter assembly influid communication with said conduit assembly and said gas componentmeasuring cell, the filter assembly disposed in an upstream positionfrom said gas inlet for filtering particulate matter from said gassample prior to analysis in said gas component measuring cell.
 14. Thesystem as claimed in claim 13, wherein said gas conduit assemblyincludes an elongated sampling probe for extracting said off-gas samplefrom a generally central portion of said furnace off-gas stream, and aheated conduit fluidically coupling said probe and said gas analyzer,the heated conduit operable to convey said extracted gas sample fromsaid probe to said gas analyzer apparatus as a heated gas sample at atemperature selected at between about 80° C. and 150° C.
 15. The systemas claimed in claim 13 or 14, wherein said gas component measuring cellcomprises first and second removable windows spaced towards each of thefirst and second ends of the sampling chambers.
 16. The system asclaimed in any one of claims 13 to 15, wherein said emitters furthercomprise a collimator operable to emit said coherent light beam energyas a collimated light beam, and said detector assembly further comprisesa lens associated with each said sampling chamber, said lens configuredto refocus the emitted collimated light beam towards the associatedoptical detector.
 17. The system as claimed in any one of claims 13 to16, wherein the plurality sampling chambers include first and secondgenerally cylindrical chambers, said first and second cylindricalchambers being provided in fluid communication along longitudinallyextending edge portions, said gas inlet being fluidically coupled tosaid first cylindrical chamber adjacent to said first chamber first end,and a gas outlet being fluidically coupled to said second cylindricalchamber adjacent to said second chamber second end.
 18. The system asclaimed in any one of claims 13 to 17, wherein said gas conduit assemblycomprises a heated gas conduit having a length selected at between about2 and 15 metres.
 19. The system as claims in any one of claims 13 to 18,wherein said gas component measuring cell is provided as a modularremovable unit.
 20. The system as claimed in any one of claims 13 to 19further comprising a pump assembly operable to convey said gas samplefrom said gas sample source through said filter assembly and into saidsampling chamber for analysis.
 21. The system as claimed in any one ofclaims 13 to 20, wherein said gas analyzer apparatus further includes acabinet comprising a heated compartment, and a heater assembly thermallycommunicating with said heated compartment, said gas component measuringcell being housed substantially within an interior of said heatedcompartment, and wherein said heater assembly is operable to maintainsaid heated compartment interior at a temperature of between about 105°C. and 140° C.
 22. The system as claimed in claim 21, wherein thecabinet further includes an unheated compartment, the pump assemblyincluding a pump motor being housed substantially within an interior ofthe unheated compartment.
 23. The system as claimed in any one of claims13 to 22, wherein said coherent light source comprises a plurality oftunable diode lasers, each said laser being provided for opticalcoupling to an associated emitter.
 24. The system as claimed in any oneof claims 13 to 23, wherein said off-gas system comprises a steel makingfurnace off gas stream, and said gas components are selected from thegroup consisting of CO, CO₂, H₂, water vapour, and O₂.
 25. A furnace gasanalysis and control system comprising, at least one gas analyzerapparatus operable to measure selected gas components of an extractedfurnace off-gas sample, a system processor electronically communicatingwith each said gas analyzer and operable to output furnace controlsignals in response to the measured gas components detected thereby, acoherent light source, and a gas conduit assembly in fluid communicationbetween a selected sampling point in said off-gas stream and anassociated said gas analyzer apparatus, each said gas analyzer apparatusincluding, a gas component measuring cell comprising, a gas inlet andgas outlet, a plurality of elongated sampling chambers for receiving theextracted off-gas sample therein, said sampling chambers fluidicallycommunicating with each other and said gas inlet, the sampling chambersextending respectively from a first end to a second end spacedtherefrom, and having a respective length correlated to an absorptionprofile the selected gas component of said off-gas sample to beanalyzed, an optical head being positioned towards the sampling chamberfirst ends, the optical head provided for optical coupling to saidcoherent light source and including a plurality of emitters, saidemitters being positioned to emit a coherent light beam along anassociated sampling chamber, a detector assembly comprising an opticaldetector positioned towards each associated sampling chamber second endfor detecting and converting non-absorbed portions of said associatedcoherent light beam into electric signals, and a filter assemblydisposed in an upstream position from said gas inlet for filteringparticulate matter from said extracted off-gas sample prior to analysisin said gas component measuring, a pump assembly operable to convey saidoff-gas samples from said selected sampling points to the gas inlet ofselected said gas analyzer apparatus.
 26. The system as claimed in claim25, wherein the at least on gas analyzer apparatus includes a firstanalyzer apparatus and a second analyzer apparatus, the coherent lightsource comprises a plurality of tunable diode lasers, and a switchingassembly operable to selectively optically couple said lasers andassociated one of said emitters of a selected one of said first andsecond analyzer apparatus.
 27. The system of claim 25 or 26, whereinsaid gas component measuring cell comprises first and second removablewindows spaced towards and substantially sealing respectively each ofthe first and second ends of the sampling chambers, and each of thesampling chambers comprising a generally co-axially aligned cylindricalchamber, the sampling chambers being in fluid communication alonglongitudinally extending adjacent edge portions.
 28. The system asclaimed in any one of claims 25 to 26, wherein said emitters furthercomprise a collimator selected to emit said coherent light beam as acollimated light beam along said associated sampling chamber, and saiddetector assembly further comprises a lens associated with each saidsampling chamber for refocusing each said collimated light beam towardsan associated said detector.
 29. The system as claimed in any one ofclaims 25 to 28, wherein said gas conduit assembly comprises anassociated heated gas conduit providing fluid communication between eachselected sampling point and each associated said gas analyzer apparatus,each associated heated gas conduit having a length selected at betweenabout 2 and 15 metres.
 30. The system as claimed in any one of claims 25to 29, wherein said gas component measuring cell is provided as areplaceable modular unit.
 31. The system as claimed in any one of claims24 to 29, wherein each gas analyzer apparatus is housed substantiallywithin an associated cabinet, each said cabinet comprises a heatedcompartment, and a heater assembly thermally communicating with saidheated compartment, said gas component measuring cell being housedsubstantially within an interior of said heated compartment, saidcabinet having width, length and height dimensions each selected atbetween about 0.1 and 2 metres.
 32. The system as claimed in any one ofclaims 25 to 31 comprising a plurality of said gas analyzer apparatus,and wherein said furnace comprises a steel making furnace, and saidselected gas component is selected from the group consisting of CO, CO₂,H₂, water vapour, and O₂.
 33. The system as claimed in any one of claims13 to 32, wherein each said gas analyzer apparatus further includes awater vapour sensor fluidically communication with said gas componentmeasuring cell for sensing water vapour concentration in said sample.34. The system as claims in claim 33, wherein said water vapour sensoris disposed in said heated compartment of said cabinet.
 35. Use of afurnace gas analysis and control system comprising, a plurality of theoff-gas analyzer apparatus as claimed in any one of claims 1 to 12, atleast one coherent light source for optically communicating coherentlight to the off-gas analyzer apparatus, and a system processorelectronically communicating with each said off-gas analyzer apparatusand the at least one coherent light source, wherein, the gas conduitassembly of a first said off-gas analyzer being provided in fluidcommunication with a first sampling location along a furnace off-gasfume duct for receiving associated extracted gas samples therefrom, andthe gas conduit assembly of a second said off-gas analyzer beingprovided in fluid communication with a second sampling location alongthe furnace off-gas fume duct for receiving associated extracted gassamples therefrom, and wherein said second sampling station is spacedfrom said first sampling station, and wherein in use, following theextraction and communication of the associated extracted gas sample,into the sampling chambers of the first gas analyzer, with said systemprocessor, actuating said first off-gas analyzer to emit coherent lightbeams from at least one said coherent light source along the samplingchambers, and by the detector assembly, detecting and measuring theemitted coherent light beams in the sampling chambers as an absorptionprofile of an associated target off-gas component selected from thegroup consisting of N₂, CO, CO₂, H₂, O₂ and water vapour at said firstsampling locations, and following the extraction and communication ofthe associated extracted gas samples to the sampling chambers of thesecond gas analyzer, with the system processor, actuating said secondoff-gas analyzer to emit coherent light beams from at least one saidcoherent light source along the sampling chambers, and by the detectorassembly, detecting and measuring the emitted coherent light beams as anabsorption profile of the associated target off-gas component at saidsecond sampling location, and comparing the measured absorption profilesof the target off-gas components to the first and second samplinglocations, and generating furnace control signals based on thecomparison.
 36. Use of the furnace gas analysis and control system asclaimed in claim 35, wherein the system processor is operable topreferentially actuate one or more of said off-gas analyzers byincreased time and/or frequency to effect a gas sample analysis which isweighted to one or more sampling locations along the furnace off-gasfume duct.
 37. Use of the furnace gas analysis and control system asclaimed in claim 35 or claim 36 further wherein during actuation of thefirst off-gas analyzer, maintaining a temperature in the samplingchambers above a dew point of the associated extracted gas sample, andwherein at least one associated target off-gas component comprises watervapour.
 38. Use of the furnace analysis and control system as claimed inany one of claims 35 to 37, wherein the furnace gas analysis and controlsystem further includes an optical switching assembly operable toselectively optically couple at least one said coherent light source andthe optical head of the first off-gas analyzer and/or the second off-gasanalyzer, the system processor being operable to selectively actuate aselected one of the first and second off-gas analyzer apparatus, andoperating the optical switching assembly to optically couple the atleast one coherent light source to each of the first and second off-gasanalyzer when selectively actuated.
 39. Use of the furnace gas analysisand control system as claimed in any one of claims 35 to 38, whereinsaid coherent light source comprises a tunable diode laser.
 40. Theapparatus as claimed in claim 1, wherein the coherent light sourcecomprises a multiplexed laser beam.